The use of various bismuth salts as a catalyzing and/or corrosion protection constituent in lead-free CED coating agents is described repeatedly in the patent literature, for example, in U.S. Pat. Nos. 5,936,013, 5,702,581, 5,554,700, 5,908,912, 6,174,422, 5,670,441, WO 96/10057, U.S. Pat. No. 5,972,189, WO 00/50522, U.S. Pat. No. 6,265,079, EP 1 041 125, WO 00/47642, WO 01/51570.
WO 00/64991 discloses CED coating agents which contain yttrium compounds as the corrosion protection constituent.
None of the above-stated literature references discloses the simultaneous use of bismuth salts and yttrium and/or neodymium compounds in CED coating agents.
One problem in CED coating is the loss of edge coverage when baking the CED coating layer previously deposited onto an electrically conductive substrate. On baking, the CED coating layer draws back from the edges of the substrate, becoming thinner at or in the immediate vicinity of the edges. In extreme cases, edge coverage is inadequate after baking and the corrosion protective action on or in the area of the edges is impaired or lost. Hitherto, known measures for improving the edge protection of CED coating layers, such as the addition of high molecular weight binders or microgels to the CED coating agent or increasing the pigment content in the CED coating agent, all share the disadvantage of increasing the roughness of the baked CED coating layer.
The object of the invention is to provide CED coating agents with good corrosion protection and good edge corrosion protection. The CED coating agents should on deposition and baking provide CED coating layers having a low roughness. In the case of a subsequent coating to be applied onto the CED coating layers, for example, a multi-layer coating as conventional in automotive coating, low roughness of the CED coating layer acting as corrosion protection primer is a favorable precondition for a good appearance of the outer surface of the subsequent multi-layer coating.